1. Field of the Invention
The present invention generally relates to equipment for cutting depressions in highway surfaces to provide ways of alerting motorists of road edges and centerlines and, more particularly, is concerned with a machine and method for repetitively cutting depressions in a highway surface having substantially equal dimensions and being substantially equally spaced apart from one another.
2. Description of the Prior Art
To make highways as safe as possible, one common practice has been to install safety markers and reflectors of various kinds along edges and centerlines of highways. These devices are designed to reflect light from a vehicle's headlights back to the driver or to make a sound when the vehicle's wheels ride over the devices, or to do both, in order to alert the driver of the vehicle's location on the highway and thereby compensate for a driver's inattention or bad driving weather.
Different machines have been proposed in the prior patent art to cut depressions in the highway surface for receiving and seating these safety markers and reflectors. Representative examples of prior art machines are disclosed in U.S. Pat. Nos. to Kennedy (4,797,025) and Sergeant (4,900,094).
The Kennedy patent discloses a self-propelled machine which has hydraulic drive wheels, a frame plate raised and lowered by a hydraulic cylinder with a piston rod, and cutter blades supported from and forwardly of the frame plate. Connected to and forward of the cutter blades are a pair of cams which rotate on the roadway and raise and lower the cutter blades into and out of cutting relation with the roadway to control the shape and length of the depression as the machine is moved forward over the roadway. Weights on the cams ensure that the cams are in proper position for the start of each cut. The cutter blades and drive wheels are interconnected and hydraulically driven by an automatic flow control circuit which functions to slow down the forward movement of the machine when the rotary cutter blades encounter difficult cutting. Thus, the cutter blades always operate at the same optimum cutting speed and efficiency, while the cams control the shape and length of the depression as the machine is moved forward over the roadway.
The Sergeant patent discloses a machine in the form of a framework attached to the rear of a truck, a pair of spaced apart cutters, and an arm and cylinder pivotally mounted on the framework and supporting the plunge cutters. The cylinder is operable for raising and lower the cutters relative to the roadway. Water and air supplies are directed at the cutters to cool and lubricate the cutters and clean out the depressions made in the roadway.
More recently, a growing number of highway authorities have decided to add depressions called "rumble strips" along the side edges of the highway so as to alert drivers that they are approaching the edges of the road. These rumble strips take the form of a series of depressions in the highway surface which do not employ safety markers or reflectors. Instead, the dimensions of and spacing between the depressions are very precisely designed to produce a repetitive noise when ridden over by a vehicle wheel which is sufficiently audible to awaken a motorist who has fallen asleep. For instance, the dimensions of each depression is sixteen inches in width, seven inches in length, and one-half inch in depth. The spacing between adjacent depressions is five inches. Also, the profile of the depressions must be uniform from one to the next and the depressions aligned the same with the edge of the road.
A machine for fabricating highway rumble strips must be capable of cutting depressions in a repeatable and reliable manner having the prescribed precise dimensions and spacing. The machines of the Kennedy and Sergeant patents, are incapable of doing so. Consequently, a need still exists for improvements in techniques for cutting depressions in highway surfaces which will provide the repeatability and precision requires to make rumble strips that meet highway standards.